Double-acting hydraulic press



De@ 26,1939. w. ERNST DOUBLE-ACTING HYDRA`UL1C PRESS Filed May 27, .1936 2 sheets-sheet 1 Dec. 26, 1939. w. ERNST DOUBLE-ACTING HYDRAULIC PRE Filed May 2'7.- 1936 F/q. s.

Sheets-Sheet 2 l e 12a /2a INVENTOR il 7E@ ERNST.

ATTORNEYS Patented Dec. 26, 1939 UNITED Y STATES DOUBLE-ACTIN G HYDRAULIC PRESS walter Emst, Mount Gilead, om, assignor to The Hydraulic Press Corporation, Inc., Wilmington, Del., a corporation of Delaware Application May 27,1936, Serial No. 82,087 13 Claims. (Cl. 113-45) This invention relates to hydraulic: presses and control circuits therefor.

One `object of this invention is to provide a' hydraulic press having a clamping plunger 'andl a drawing plunger with a control circuit arranged to cause the main plunger and the clamping plunger to advance simultaneously without the possibility c." the main plunger getting ahead of the clamping plunger.

Another object is to provide such a press and circuit, wherein means is provided to prevent the main plunger from starting the drawing operation until the clamping plunger has engaged the work-piece with a suflicient pressure.

Another object is to provide such a press and circuit, wherein .neans is provided for permitting the main plunger to carry out the drawing operation as soon as a predetermined pressure has been built up in the clamping plunger cylinder l by the engagement of theclamping plunger with the work-piece.

Another object is to provide such a press and circuit, wherein means is provided for releasing the pressure in the clamping plunger cylinder in immediate response to the reversal of themain plunger so as to prevent possibility of shock or strain due to the main plunger picking up` the clamping plunger slide before the pressure in the clamping plunger has dropped.

i Another object is to provide an auxiliary pump control device which is responsive in its operation-to the operation of the control device of the main pump.

Another object is to provide a circuit for reni dering a valve selectively operative or inoperative, according to the setting of a main pump, which in turn, governs the control of an auxiliary pump.

Another object is to provide a surge valve i having a disabling device for temporarily and -selectively holding the valve inoperative.

Another object is to provide acombination relief and check valve which shall serve as a reliei valve in the ow of iluid in one direction, and

L as a check valve in the opposite direction. v

Another object is'to provide a double-acting drawing press having a drawing plunger and clamping plunger, with a, hydraulic circuit and devices arranged to permit the gravitational descent of the clamping plunger andy drawing plunger in exact unison with one another; with devices to delay the application of pressure to the'drawing plunger until the vpressure has been built up vto a predetermined amount in the clamping plunger cylinder, whereupon the drawing plunger is permitted to carry out its drawing operation; and-with devices to cause the release of therpressureiin the clamping plunger cylinder at the instant the reversal of the main plunger" takes place.

In the drawings: y f Figure 1 is a diagrammatic view, partly in section, of a. hydraulic drawing press and circuit, according to the present invention. Y

Figure 2 is a central vertical section through 10 the combination relief and check valve employed in the circuit of Figure l.

Figure 3 is an elevation, partly in section, of a hydraulic pump, showing the servomotor control arrangement for bringing about its reversal in l5 response to the application of pressure fluid from an outside source. Figure 4 'is an enlarged sectional viewof the main cylinder surge valve shown in Figure 1.

Hydraulic press and circuit generally Referring to the drawingsin detail, Figure l shows a circuit containing the hydraulic drawing press and the associated control devices of this invention. The` circuit a's a whole contains a number of individual units which may be generV ally designated before being described in detail. The press I0 is operated by a main pump l l, which in turn, is supplied with servomotor fluid from a servomotor pump l2, and discharges fluid into the return side of thepress I0 by way .of the combination relief and check valve i3. The press I0 is also provided with a main surge valve it, of a special type, having means incorporated therewith for holding the surge valve temporarily inoperative. The press l il is provided with ciamping cylinders having a surge valve I5 opening into the surge tank of the press i0. The surge valve i5 is opened by pressure fluid from the push-back side of the main plunger, andl is of a type described in the Ernst patent, No. 1,892,568, of December 27, 1932.

The surge tank of the press l@ also contains a check valve i6, a pressure release valve il which is arranged to control direct communication between the main cylinder and the surge tank, and a by-pass valve i8, each of these valves being provided with choke valves i9 and 20, re-l spectively. The details of the valves il, I8, i9 and 20 form no part of the presentinvention, but 5o are fully disclosed in the Ernst patent, `l\^l,o.k 1,956,758, dated May 1', 1934. The purpose of; the main Cylinder release and by-pass valve arf.k rangement il, i3 isto release pressure from thel main cylinder prior to the opening of the vsurgel 555" arranged to provide pressure fiuid for operating the clamping cylinders of the press. This clamping pump 2I is provided with a special servo-= motor control arrangementdescribed in detail below.

Press construction The hydraulic press i6 shown diagrammatically in Figure 1 is provided 'with a clamping block 22 having a die 23, with a recess 24 into which the work-piece 25 -is -to be drawn by the action of the press. Thel clamping block 22 is mounted upon the bed of the press (not shown) and is arranged to receive the outer portions of the work-piece 25, clamped thereagainst by the clamping slide 26. The clamping slide 26 is operated by the clamping plungers 21 adapted to reciprocate in clamping cylinders '28.' The clamping slide 26, atpoints adjacent the juntions therewith of the clamping plungers 21, is

provided. with projecting portions 28 adapted to be engaged by the main platen of the press upon the upward stroke thereof, as will subsequently appear. Arranged to cooperate with the die 23 and adapted to fit into the recess 24 thereof is a punch 36 attached to the main platen 3|, which in turn, is secured to the main or drawing plunger 32. The drawing plunger32 is of a double-acting type, with a piston head 33, and reciprocates within the main cylinder 34.

One of the clamping cylinders 28 is provided with an aperture 35 in the: head thereof, adapted to receive the surge valve i5 previously mentioned. Similarly, the main. cylinder 34 is prow vided with an aperture 36 for receiving the main surge valve i4, also previously mentioned. The main cylinder 34 is further provided with a port 31 leading, by way of the line 38, to the main cylinder release valve I1, from which the line 3s leads through the choke valve 20 to the by-pass valve I8. The line 46 also interconnects the main cylinder release valve I1 and the by-pass valve I6. The main cylinder release valve I1 discharges directly into the surge tank 4I of the press I6 by way of the line 42, containing the choke valve i9. The line 43 leads from the main cylinder release valve I1 to the return line 46 of the main pump Il. The check. valve I6 is installed at an `intermediate point along the line 43 and within thesurge tank 4I in order to permit uid to be drawn therethrough into the line 43 when the latter is under suction. The internal arrangement and operation of the circuit comprising the port 31, the line 38, the main cylinder release valve I1, the by-pass I8, the line 43 and the check valve I6 will be found fullS7 disclosed in the above-mentioned Ernst patent, No. 1,956,758, of May 1, 1934.

Main pump and associated circuit u reverse the discharge thereof. The servomotor 41 is controlled manually by a servomotor valve 46, containing a valve plunger 46 operated by a hand lever 50. The servomotor valve 46 is connected to the surge tank 4I by means of the pipa line 5I The servomotor 41 and servomotor valve 48 are interconnected by means of the pipe lines 52 and 53, respectively. The servomotor 41 is also automatically operated on the return stroke by a pilot piston within a` pilot cylinder 54, through the pilot line 55 running tov the return line 44 of the main pump II; and on the pressing stroke by a differential pilot piston (not shown) by way ofthe line 56, leading therefrom to the pressing line 45.

Fluid for operating the servomotor 41 is supplied from the surge tank 4I by the servomotor pump I2, connected thereto by thesuction line 51, connected to the suction side of the pump I2. The pressure side of the pump I2 is connected to the suction line 51 by means of the by-pass line 58, containing the pressure relief valve 59, and is also connected to the servomotor valve 48 by means of the pressure line 60. When the servomotor Valve 48 is moved into such a position that the pressuer line is blocked, the discharge of the pump I2 passes through the pressure relief valve 59 to the suction line 51, and is accordingly by-pressed until the line 60 is again opened by shifting the manual control lever 50.

The details of the servomotor valve 48 and thel 'servomotor 41 form no part of the present invention, and will be found fuly disclosed in the Ernst patent, No. 2,038,272, dated April 21, 193,6.

Combination relief and check valve The return line 44 from the main pump II leads to the combination relief and check valve I3, beyond which the line 6I leads to the port 62, discharging into the return side of the main cylinder 34. The valve I3 consists of a casing 63 having a chamber 64 with a port 65 closed by a ball 66. Opposite the port 65 is a plug 61 containing a bore 68, in which reciprocates the valve plunger 69. A portion 16 of the chamber 64 intersects the bore 68. vided with an enlarged portion 1I engaged by a coil spring 12, the opposite end of which engages the collar 131, acted upon by the adjusting screw 14 mounted in the threaded bore 15 of the valve cap 16. The latter is mounted upon the valve casing 63. The pipe line 44 opens into the chamber 64 by way of the port 11, whereas the pipe line 6I leads outwardly from the port 18 in the chamber 19 containing the ball 66.

Accordingly, uid xay pass freely from the ,main pump II, along the line 44, through the -valve lf3 and the line 6I,A into the return side of the main cylinder 34 by merely displacing the ball 66 from its position closing the port 65. -Fluid proceeding in the opposite direction, however, cannot pass freely, but forces the ball 66 against the port 65 to close this port.v Pressure is built up in the chamber 19 containing the ball 66 until this pressure is suflicient to force the plunger 66 upwardly against the urge of the coil spring 12, whereupon the entrapped fluid is released through the bore 68 into the extension 10 of `the chamber 64, and thence escapes through the line 4 4. The detailed operation of the combination relief and check valve I3 is described below.

Auxiliary or clamping pump The auxiliary pump or clamping pump 2| The plunger 69 is proserves to supply pressure fluid to the clamping n plungers 21 for moving the clamping slide 26, ando: is shown lin `detail in Figure 3. This pump consists ofva casing 80 containing a shift ring 8| for varyingthe eccentricity of the secondary p rotor of the pump relatively to the cylinder barrel or primary rotor, in a manner well known to those skilled in the art. By thus shifting the shift ring 8 I- the delivery of the pump 2| is varied or reversed. 'I'he shiftring 8| is mounted upon the rods 82 and 83, secured within the diametrically opposite .threaded bores 84. l

i The rod 82 passes throughthe anti-leakage packing 85and the retainingV cap 86 therefor, and is threaded upon its outer end, as at 81, to receive the nut 88 and the stop nut 89. Also threaded upon the threaded portion 81 is a sleeve 90, to whichis securedthe hand wheel 9|, as by the set screw 92 and key 93. The sleeve 90 engages the ball thrust bearing 94, the opposite side Y K of which engages a sleeve 95 arranged to comtubular-extension 91 secured to the pump casing 80 by means of the set screws 98. A lubricating coupling 99 serves to admit oil: to lubricate the connection between the sleeve 95 and its tubular guide portion 91. The sleeve 95 is not threaded upon the threaded portion 91, but is provided with a bore |00, which is spaced apart from the threaded portion 81.

To the opposite side of the pump 2| is secured a tubular portion through which passes the rod 83, and which is closed by a cap |02 having an end plate |03. The cap |02 contains a bore |04, within which reciprocates a piston head which is mounted upon the rodL 83 and retained in position by the head |06 thereof 'I'he piston head |05 is provided with an annular shoulder |01 lying within the annular chamber |08, from which the line I 09 leads, through the choke valve I I0 to the pressure side of the auxiliary pump 2|.` Also mounted upon the rod 83 is a piston head' III, adapted to reciprocate within the bore ||2` of the tubular membe` |0I.

The line ||3 leads from the bore ||2 on the left-hand side of the piston head to the servomotor line 53 interconnecting the `servomotor valve 48 with the servomotor 41 of the main pump II. 'Ihe line 53 supplies pressure uid from the servomotor pump I2 to the servomotor 41 to reverse the main pump and cause it to deliver pressure iluid through the return line 44 to the return side of the main cylinder 34. When this is done it will be obvious that pressure uid will also flow through the line ||3 into thebore ||2, and act upon the piston head forcing it to the right (Figure 3), and causing it to engage the piston headA |05 and force the rod 83 and shift ring 8| of the pump 2| to the right, in a manner subsequently to be described in connection with the operation of the circuit as a whole.

The auxiliary pump 2| is supplied with -uid v from the surgetank 4| by way of the suction line I I4, and discharges pressure iluid from its pressure side through the pressure line' I5 andthe ports ||6, into the clamping cylinders 28 above the clamping plungers v21. From the.bore |04 the port ||8 opens intov the line ||9, which leads to' the main Vsurge valve I4 to render the latter operative or inoperative, in the manner described below. v l

`within the counter-bore |31. of the counter-bore |31 is closed by a cap |38 Main surge valve v 'I'he main surge valve (Figure 4) *consistsy of a. tubular casingv|20 mounted in the bore 36in the head of the main cylinder 34and containing an end cap |2I. 'Ihe tubular casing |20 is provided with outlet ports |22 leading from the interior into the chamber formed by the main cylinder 34 above the main piston head 33. The end cap |2I is provided with a projection |23, serving as a seat for the coil spring |24, the opposite end of which urges upwardly the surge valve member I 25. The latter is provided with a beveled portion |26 adapted to engage a valve seat |21 in the casing |20, and is also provided with uted portions |28 pass through the passageway |29, by way of the uted portions |28, between the valve seat |21 and the beveled portion |26, through the ports |22 into the main cylinder, andvice versa, when the main surge valve I4 is open.

Mounted above the tubular casing is a cylindrical casing |30 having a flanged portion |3| `resting upon the outer wall of the main cylinder 34, and provided with passageways |32 leading from the surge tank into the interior of the valve (Figure 4). The cylindrical casing v|30 is provided with a bore |33, within which the valveoperating rod |34 is reciprocably mounted.4 The rod |34 is provided'with a head |35, urged in an upward direction by the coil spring |36 contained The upper portion having a bore |39 within which reciprocates a piston rod |40, having an annular shoulder |4| formed by a piston head |42. The piston head |42 reciprocates within a bore |43, access Vto which is 'gained through the port |44 leading to the pipe line I |9. Above the piston head |42 is an annular enlargement |45, urged downwardly by the coil spring l|46 within the chamber |41. The opposite end of the coil spring |46 engages the end, wall |48 containing the port |49 opening into the pipe line |50. The latter leads to the pipe line 43, and is joined at an intermediate point by the pipe line |`5| leading thereto from the surge valve I5. When the main pump II is set to discharge pressure fluid into the return side of the main cylinder 34, as will subsequently appear, pressure fluid likewise passes along the lines |50 and |5| to operate the surge valves I4 and I5. Operation In the operation of the press and circuit shown in Figure 1, a work-piece 26,-inthe iorm of a metal blank, is placed upon the clamping block 22 immediately above the die 23. The main pump and auxiliary pump 2| are then started in operation, and the hand lever 50 is set at such .a

position that pressure fluid is delivered from the servomotor pump I2,v through the servomotor vvalve 48 and the line 52, into the servomotor cylinder 41 to operate the servo-piston to shift the shift ring of the main pump to a forward deit through the pressure line H6, through the 76 ports III into the space above the clamping plungers 21.

The weight of the clamping slide, the clamping plungers 21, the main platen 3| and the main plunger 32 causes these parts to descend under.

the influence of gravity, opening the surge valves |4 and I5 and permitting uid to pass directly from the surge tank 4| into the clamping cylinders 28 and main cylinder 34. In the main surge valve I4 this fluid passes through the passageways |32, the iluted portions |28, the space between the valve seat |21 and'beveled portion |28 and the ports |22 vinto the 'main cylinder 34, the suction created therein drawing the surge valve member |25 downwardly against the urge of the coil spring |24 (Figure 4). The interior arrangement of the surge valve' I5 and its action in this respect are similar to the arrangement of the lower portion of the main surge valve shown in Figure 4. In this way the descent of the clamping plungers 21 and main plunger 32 is brought about more rapidly than would be possible by the use of pressure uid discharged fromthe main pum`p II and auxiliary pump 2| without the action of the surge valves I4 and I5.

At this point, ho'wever, it is necessary that the clamping slide 26 and main platen 3| descend in.

' main plunger assembly and clamping plunger assembly, acting upon the uid entrapped beneath the main piston head 33, will be just suflicient to move the relief valve plunger 89 to open the valve. The clamping plunger assembly can never move ahead of the main plunger assembly because of the shoulders 29. The instant the main plunger assembly tends to move'ahead of the clamping plunger assembly, however, the relief valve plunger 69 will close, because the weight of the main plungr assembly is insumcient to keep it open without the added weight of the clamping plunger assembly. For this reason also, the instant that the clamping plunger assembly engages the work-piece 25 and halts, the main plunger assembly will also haltl until pressure is built up in the main cylinder 34 sumcient to open the valve plunger 69 of the Valve I3. Obviously, the seating of the ball 36 will prevent iluid from passing from the chamber 19, through the port 05, into the chamber 64 (Figure 2).

Meanwhile, the auxiliary pump 2| has been operating and discharging uid into the clamping cylinders 28. As the clamping slide- 28 comes to rest against the work-piece 25,'pressure is built up by the pump 2| within the clamping cylinders 28, and this pressure is communicated, through the line |09 and the choke valve ||0 (Figure 3) .to the annular' chamber |08, where it acts against the annular shoulder |01 upon the piston head |05, causing the piston head |05 to move to the right, overcoming the contrary urge of the coilsprlng 06 on the opposite side of the pump 2|. The coil spring is so arranged as to urge the shift ring 8| of' the pump 2| to the left, into its m11 forward delivery position. As the piston head |05, acting against the head |08 on the rod 83, forces the latter to the right, it moves the shift ring 8| to the pump. At the same time the piston head |08 eventually moves beyond the port I|8 and opens communication between the lines |09" and II9, permitting pressure iiuid to ilow through the latter into the chamber |43 of the main surge' valve I4 (Figure 4), where it acts against the annular shoulder I4| Vto lift the piston head |42 against the urge-of the coil spring |48. This lifts the piston rod |40 and permits the operating rod |34 to rise by the urge of .its coil spring |38, thereby permitting the surge valve |25 to close by moving upwardly.

Any excess discharge of the main pump II into the main cylinder 34 above the piston head 33 which might have otherwise served to force the main plunger 32 to move ahead of the clamping plungers 21 has, in the meantime, been discharging through the ports |22, the iluted portions |28 and the passageways |32 into the surge tank 4| so that no excess pressure could build up within the main cylinder 34. Theclosing of the main surge valve I4, however, by the action of the :duid passing along the line I I9 from the auxiliary pump 2| enables the main pump I I to accumulate pressure within the main cylinder 34 only after a suiiicient clamping pressure has been accumulated within the clamping cylinders 28. In this manner it is impossible for the main plunger 32 to get ahead of the clampingcplungers 21 or to start a drawing operation before the clamping plungers 21 have fully engaged the work-piece 25.

As previously stated, the mainv plunger 32 Vcould not advance f urther by gravity because it lacks suillcient force to open the relief valve plunger 69 in the combination relief and check Valve I3,and -it could not advance upon pump pressure because the main surge valve I4 was kept open under the action of the piston rod |40, forced 'downwardly by its coilspring |46. Not until this `piston rod |40 is withdrawn by the pressure fluid reaching it from the line II9 is it possible. to build up pressure within the main cylinder 34 to perform the drawing stroke.

At this juncture the clamping slide 28 has come to rest, clamping the work-piece 25 between it and the` clamping block 22, and the main platen 3| and punch 30 have also come to rest. By reason of the closing of the main surge valve I4, pressure now is built up within the main cylinder 34 by` the main pump until the punch 30 is forced downwardly against the work-lpiece 25, performing the drawing operation and forcing it into the recess 24 in the die 23.

When thisoperation is completed it is necessary to reverse the operation of the press and withdraw the clamping plungers and main plunger. In order to relieve the pressure in the clamping cylinders 28 before the main platen 3| picks up the clamping slide 26 by engaging the shoulders 29, the control devices associated with the auxiliary pump 2| come into play. When the hand lever 50 is lshifted to throw the main pump II into a reverse delivery position, pressure iluid is discharged into the servomotor line 53 from the servomotor valve 48, and operates the servo-piston within the servomotor cylinder 41 to accomplish this. A part of this pressure, however, passes along the line II3, into the space to the left of the piston head of the auxiliary pump 2|, moving the piston head III to the right and causing it'to shift the rod 83 and the shiftring 8| to .the right. The shift ring 8| thereby moves through the neutral delivery position of lthe auxiliary pump 2| into the reverse position thereof, thereby gagement at the shouldered 3| engages the shoulders 29 ofthe clamping slide 26.v The pressure fluid from the main pump is discharged through the return line 4:4, the combination relief and check valve |3` and the line 6|, into the space beneath the main piston head 3.3, raising vthe main plunger 32 and retracting the main platen 3 I and the clamping slide 26 simultaneously by their interenportions 29 of the clampingslide 26.`

The instant the mainpump is reversed to retract the main plunger 32,. pressure fluid passes along the lines 44, 43 and |50. and |5| to the main and clamping cylinder surge valves |4 and I5, respectively. This iuid (Figure f4) acts against the upper end of the piston rod |40 within the chamber |41, and forces it'downwardly, opening the surge valve member |25 e and permitting the uid to escape from thel top of the main cylinder 34 directly intof the surge tank 4|. At the Sametime the surge valve I5 will be` opened by the it along the line |5I, permitting the escape of the fluid from the clamping cylinders 28 Vinto the surge tank 4|, as described in the previously mentioned Ernst patent, No. 1,892,568, of December 2'7, 1932.

It will be understood that `I desirev to comr prehend within myinvention such modifications as come within the scope of the claims and the invention.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In combination, a main plunger, a clampingv plunger, a plurality of pumps for supplying pressure fluid to said main plunger and said clamping plunger, afluid tank, surge valve means for said plungers to permit gravitational descent thereof, and means associated with one of said plungers for causing it to descend in alignment with the other plunger.

2. In combination, a main plunger, a clamping plunger, a plurality of pumps for supplying pressure fluid to said main plunger and said clamping plunger, a fluid tank, surge valve means for said plungers to permit gravitational descent thereof, and a pressure-responsive valve adapted to release fluid from beneath one of said plungers to retard the descent thereof.

3. In combination, a main plunger, a clamping plunger, a plurality of pumps for supplying pressure fluid to said main plunger and said clam; ing plunger, a fluid tank, surge valve means for said plungers to permit ,gravitational desceni thereof, means associated with one of said plungers adapted during its descent to engage the other plunger, and a pressure-responsive valve adapted to release uid from beneath one of said plungers to retard the descent thereof.

4. In combination, a main plunger, a clamping plunger, a plurality of pumps for supplying pressure fluid to said main plunger and said clamping plunger, a uid tank, surge valve means lfor said plungers to permit gravitational descent thereof, means associated with one of said plungers adapted during its descent to engage the other plunger, anda pressure-responsive valve adapted to release fluid from beneath one of said plungers to retard the descent thereof, said valve being adapted to open and pass fluid therethrough under the pressure from the combined weights of said plungers and their @SSOlted pressure uid reaching voving parts yet to remain closed lunder the pressure from one plunger only. f

5.- In combinatiom a main plunger, alclamping plunger, a plurality of pumps for supplyingpressure fluid' to said main plunger and said clamping plunger, 'ailuid tank. surge valves f -isaidl plungers to permit gravitationalv descent 'e'reof means associated with' one of said plinfgersV adapted during its descent to engage the 'other plunger, and means for maintaining one of said surge valves open during the building up of pressure against the plunger lof the' other surge valve. I

6. yIn combination, a main plunger, a clamping plunger, a plurality of pumps for supplying pressure fluid to said main plunger and said clamping plunger, a fluid tank, surge valves for said plungers topermit gravitationaldescent thereof, means associated with one of said plungers adapted during its descent to.A engage the other plunger, meansA for maintainingr'rnel of said surge valves openduring the building .up ofpressure against the plunger of the othersurge` valve, and means responsive to the` attainment of al predetermined pressure in saidlast-mentioned surge.valvey to close the open surge valve.

, e '7.4` In combination, a double-acting main plunger, a main pump connected toboth .sidesl of said plunger, means for reversing the flow of fluid between said main pump and said mainplunger,y

a clamping plunger, an auxiliarypump therefor,

f said main plunger` and said clamping plunger being initially advanceable by gravity andsaid clamping plunger being engageable'with said `main plunger during this initial advancement of said plungers, means for reversing the iow of fluid between said auxiliary pump and said clamping plunger, means responsive ,to thev operation of said main pump-reversing means for operating said auxiliary pump-reversing means, and a valve in the line connecting lthe main` pump to the reverse side of the main plunger and adapted to open and pass fluidfi'reely in one direction and to open and pass fluid in the opposite direction in response to the attainment of a predetermined vpressure corresponding to and resulting-from the combined weights of said main plunger and said clamping plunger while in engagement during their initial advancement, the weight of either of said plungers separately being ineifective to open said valve whereby to prevent the main plunger from advancing ahead of the clamping plunger.

8. In combination, a double-acting main plunger, a main pump connected to both sides of said plunger, means for reversing the delivery of uid from said main pump to said main plunger, a clamping plunger, an auxiliary pump therefor,

' said main plunger and said clamping plunger being initially advanceable by gravity and said clamping plunger being engageable with said main plunger during this initial advancement of said plungers, means for reversing the flow of fluid from said auxiliary pump to said clamping plunger, and a valve in the line connecting the main pump to the reverse side of the main plunger and adapted to open and pass fluid freely in one direction and to open and pass fluid in the opposite direction in response to the attainment of a predetermined pressure corresponding to and resulting from the combined weights of said main plunger and said clamping plunger while in engagement during their initial advancement, the weight of either of said plungers separately being lneiective to open said valve whereby to prevent 'l the main plunger from advancing ahead of the clamping plunger.

9. In combination, a reversible hydraulic machine, a hydraulic pump for operating one portion of said machine, means for reversing the flow of uid between said pump and said machine,

a second hydraulic pump for operating another portion of said machine, said second pump having a reversing member for reversing the delivery 10 thereof, a pilot cylinder, a pilot piston in said J cylinder connected to shift said reversing member,v

, means responsivev to thel reversal of iluid flow between said rst pump and said machine to admit pressure fluid to said pilot cylinder to shift said reversing member and reverse the delivery of said second pump, and a second pilot piston arranged 'to shift said reversing member into the neutral delivery position of said second pump in response to the building up of 4a Vpredetermined pressure in the circuit of said second hydraulic pump.

10. In combination, a hydraulic press having a main cylinder, a main plunger therein, a clampin g cylinder, a clamping plunger therein, a surge valve for said main cylinder, a pump to supply pressure fluid to said main. cylinder, another pump to supply pressure fluid to said clamping "cylinder, a pilot piston for moving the flow-control element of said clamping cylinder pump, a pilot cylinder therefor, means for admitting pressure iiuid to said pilot cylinder, a hydraulically operated member for closing said surge valve, and means opened by the motion of said pilot piston for transmitting fluid to operate said surge valve member to close said surge valve.

l l1. In combination, a hydraulic press having a main cylinder, a main plunger therein, a clamping cylinder, a clamping plunger therein, a surge valve for said main cylinder, a pump to supply -pressure fluid to said main cylinder, another pump to supply pressure fluid to said clamping cylinder.' a pilot piston for moving the now-control-element of said clamping cylinder pump, a pilot cylinder therefor, yielding means urging said pilot piston in -one direction, means for ads mitting pressure uid from said clamping dcylinder for moving said pilot piston in the.opposite direction in proportion to the pressure built up in said clamping cylinder, a hydraulically operated member for closing said surge4 valve, and means opened by the motion of said pilot piston for transmitting iluid to operate said surge valve member to close said surge valve.

l2. In combination, a reversible hydraulic machine including at least two hydraulic motors, a ilrst reversible variable delivery hydraulic pump connected to operate the rst motor of said machine and including a reverseiy shiftable flow control member for reversing the ow of uid between said pump and said first motor, a second reversible variable delivery hydraulic pump'connected to operate the second motor of said machine, said second pump having a second reverse- 1y shiftable ilow control member for reversing the delivery thereof, a hydraulic device connected to shift said second iiow control member, and means responsive to the reversal of said first pump for supplying pressure uid to saidhydraulic device to reverseiy shift said second ilow control member and consequently to reverse the delivery of said second pump. y

13. In combination, a reversible hydraulic ma chine including at least two hydraulic motors, a first reversible variable delivery hydraulic pump connected to operate the first motor of said machine and including a reverseiy shiitable flow control member for reversing the ow oi.' iluid between said pumpand said ilrst motor, a second reversible variable delivery hydraulic pump connected to operateV the second motor of said machine, said second pump having a second reverse# ly shitable flow. control member for reversing the delivery thereof, a pilot cylinder, a pilot piston in said cylinder connected to shift said ilow control member of said second pump, and means responsive to the reversal of said first pump for supplying pressure uid to said pilot cylinder to reverseiy shift said pilot piston and said second 'ilow control member and consequently to reverse 

